Difference between revisions of "W4504 Capture the Flag IV"
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This challenge seems to expect us to convert this decimal number into Ascii. The Ascii protocol gives each character a corresponding number that can be expressed in decimal. However, the decimal number we are given is too big to represent any individual character, so we can guess that this decimal number is multiple decimal representations of Ascii characters combined. The hint also tells us this. We don't need to manually separate the different Ascii codes, however. Online decimal to Ascii converters often have a feature to guess where the spaces are supposed to be, and they are reasonably accurate. When we put the given decimal number into a decimal to Ascii converter, we get '''ahsCTF{d3cim@l_t0_ascii}'''. | This challenge seems to expect us to convert this decimal number into Ascii. The Ascii protocol gives each character a corresponding number that can be expressed in decimal. However, the decimal number we are given is too big to represent any individual character, so we can guess that this decimal number is multiple decimal representations of Ascii characters combined. The hint also tells us this. We don't need to manually separate the different Ascii codes, however. Online decimal to Ascii converters often have a feature to guess where the spaces are supposed to be, and they are reasonably accurate. When we put the given decimal number into a decimal to Ascii converter, we get '''ahsCTF{d3cim@l_t0_ascii}'''. | ||
== Forensics == | |||
=== JPG or not JPG === | |||
<pre> | |||
[75 Points] | |||
</pre> | |||
The challenge also provides a file called download.jpg. | |||
When we attempt to open download.jpg, it is unable to be displayed. This implies that the file is broken in some way. We can open this file up in a hex editor such as HxD to analyze the raw hex. When we look at the end of the file, we see some plaintext. The plaintext reads '''ahsCTF{123ddd_7sf3bq4f}'''. | |||
Revision as of 16:50, 10 February 2021
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Coming Soon |
| This page will serve as a writeup for the problems from cybersecurity CTF 4 |
Cryptography[edit]
Base64[edit]
[25 Points] Vm0wd2QyUXlWa2hWV0doVVYwZG9jRlZ0TVc5V1JsbDNXa1JTVjFac2JETlhhMUpUVjBaS2RHVkVRbHBOTTBKSVZtcEdTMk15U2tWVWJHaG9UV3N3ZUZadGNFSmxSbVJJVm10a1dHSkdjRTlaYlRGdlZWWmtWMXBJY0d4U2JHdzBWa2MxVDFsV1NuUlZia0pYWVRGd2FGcFdXbUZqTVd0NllVWlNUbFpVVmtwV2JHUXdWakZrU0ZOcmJGSmhlbXhYV1d4b2IxWXhjRlpYYkhCc1VtMVNNRnBGV2s5VWJFcEhWMnBhVjJGcmEzaFdha3BIVWpGT2RWVnNXbWxTTW1oWFZtMTBWMU14VWtkVmJrNVlZbFZhV0ZsclpGTmxWbGw1WlVWT1YwMXJWak5aTUZwVFZqRmFWMk5HVG1GU1JWcEVWbGQ0UTFaVk1VVk5SREE5
Based on the challenge name and the given encoded message, we can assume that this message is encoded using base 64. We can decode this message from base 64 using an online tool. When we decode the given message we get another string that looks like base 64. We can decode this new encoded message as well. We will repeat this process several times until we decode this message:
YWhzQ1RGe0JAczNfNjR9
The result of decoding this is ahsCTF{B@s3_64}.
Decimal to Ascii[edit]
[50 Points] Convert this to ascii. 971041156784701231005199105109641089511648959711599105105125 Hint: You need to figure out where to put spaces in the string
This challenge seems to expect us to convert this decimal number into Ascii. The Ascii protocol gives each character a corresponding number that can be expressed in decimal. However, the decimal number we are given is too big to represent any individual character, so we can guess that this decimal number is multiple decimal representations of Ascii characters combined. The hint also tells us this. We don't need to manually separate the different Ascii codes, however. Online decimal to Ascii converters often have a feature to guess where the spaces are supposed to be, and they are reasonably accurate. When we put the given decimal number into a decimal to Ascii converter, we get ahsCTF{d3cim@l_t0_ascii}.
Forensics[edit]
JPG or not JPG[edit]
[75 Points]
The challenge also provides a file called download.jpg.
When we attempt to open download.jpg, it is unable to be displayed. This implies that the file is broken in some way. We can open this file up in a hex editor such as HxD to analyze the raw hex. When we look at the end of the file, we see some plaintext. The plaintext reads ahsCTF{123ddd_7sf3bq4f}.
